Paul Bunyan Among Offshore Steel Structures

Serial Information: Civil Engineering—ASCE, 1976, Vol. 46, Issue 4, Pg. 51-52

Document Type: Feature article


The world's two largest drydocks, the larger 1,150 x 800 ft in plan were used to assemble on land the four steel jackets. They now stand in the North Sea in about 400-ft of water (about 150-ft deper than ever before). Fabrication tolerance was only 1/4-in., yet even lying on its side, one of these Forties Field jackets is up to 200 ft. high. So all possible work was prefabricated nearer the ground. This required crane lifts of some massive pieces, up to 930 tons. For this purpose 800-ton capacity tower cranes were built, that were moved by jacking along tracks of plastic-coated stainless steel sheets. Rather than designing the structure as a self-floater, or barging it to the site, a unique compromise was developed — auxiliary flotation tubes that were fastened to the jacket were upended from each platform. A sea-bottom pipeline will carry the oil the 110-miles to Scotland. Innovations in safety precautions on this pipeline: a circumferential cut nearly through the concrete gravity jacket to ease bending, and a circumferential steel band every 30-ft to 60-ft to prevent buckling along the pipe.

Subject Headings: Offshore structures | Steel structures | Steel pipes | Cranes | Land use | Prefabrication | Jacking | Plastics | North Sea | Scotland | United Kingdom | Europe

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